1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus configured to write a pattern on a substrate such as a wafer, a mask, or a reticle by using a plurality of charged particle beams.
2. Description of the Related Art
With an advancement in semiconductor production technology achieved in recent years, a great reduction in circuit pattern size and a great increase in integration density have been achieved. In such a situation, there is a great need for an increase in throughput to achieve higher productivity.
Thus, there is also a need for higher throughput in direct writing technology, which is a technique to directly write a pattern on a substrate using a charged particle beam and which is one of candidates for next-generation lithography technology.
To meet the above requirement in charged particle beam writing apparatuses, there is a trend toward increasing an area that can be irradiated with a charged particle beam at a time. An example of the charged particle beam writing technique is a point beam technique in which a charged particle beam generated in the form of a point in cross section is used. Another example is a variable rectangular beam technique in which a charged particle beam generated in the form of a variable rectangle in cross section is used. However, it is clear that these techniques are not suitable for mass production because they do not provide a high throughput in writing fine patterns with a high density. In another technique known as a cell projection technique, a particular pattern that appears frequently is written using a charged particle beam formed in a shape corresponding to the particular pattern using a cell mask. This technique is effective in particular for semiconductor circuits such as memory circuits in which the same pattern appears periodically. However, for semiconductor circuits such as logic circuits having patterns with low periodicity, it is necessary to prepare a cell mask for a large number of different patterns, which is practically difficult to achieve.
To solve the above problems, a particle beam writing apparatus of a multibeam type has been proposed (see, for example, Japanese Patent Laid-Open No. 2001-267221, Japanese Patent Laid-Open No. 2002-319532, and Japanese Patent Laid-Open No. 2005-116743). In the charged particle beam writing apparatus of this type, a substrate is irradiated with a plurality of charged particle beams. The substrate is scanned by the beams while simultaneously deflecting the plurality of charged particle beams. A pattern is formed by controlling the plurality of charged particle beams individually depending on the pattern to be written while scanning the beams across the substrate. This charged particle beam writing apparatus is capable of forming an arbitrary writing pattern without using a mask and can provide a large angle field that covers a large writing area, and thus an improvement in throughput can be achieved.
Referring to FIG. 7, an example of a multibeam-type charged particle beam writing apparatus is described below.
A charged particle beam emitted from an electron gun (not shown) is focused as a crossover image 101 and is passed through a condenser lens 102 to obtain a collimated charged particle beam 101a. An aperture array 103 has a plurality of openings 103a arranged in the form of a two-dimensional array. A lens array 104 has a plurality of electron lenses arranged in the form of a two-dimensional array. Deflector arrays 105, 106, and 107 each have a plurality of deflectors arranged in the form of a two-dimensional array. Each deflector can be controlled independently.
The charged particle beam 101a is divided into a plurality of charged particle beams 101b by openings 103a of the aperture array 103. Each of the plurality of charged particle beams 101b formed is passed through a corresponding electron lens of the lens array 104 thereby forming an intermediate image 101c of the crossover image 101 at a height corresponding to the deflector array 107. In this process, the deflectors of the deflector arrays 105 and 106 are controlled individually such that the intermediate image 101c of each charged particle beam 101b passes through a predetermined location in the deflector array 107.
The deflector array 107 controls the plurality of charged particle beams 101b to fall on a substrate 115 or to be blocked independently for each of the plurality of charged particle beams 101b. That is, a charged particle beam 101b that is deflected by the deflector array 107 is blocked by a blanking aperture (blocking plate) 109 and does not reach the substrate 115. On the other hand, a charged particle beam that is not deflected by the deflector array 107 passes through an opening 109a of the blanking aperture 109 via an electron lens 110 and reaches the substrate 115 via electron lenses 111, 112, and 113. A deflector 114 deflects charged particle beams in a direction perpendicular to a scanning direction of a stage 116.
Referring to FIG. 8, the deflector array 107 is described in further detail below. Note that, for simplicity, the electron lens 110 in FIG. 7 is not shown in FIG. 8. Charged particle beams 201, 202, and 203 are controlled by deflectors 251, 252, and 253 of the deflector array 107 in such a manner as described below. When the deflectors 251 and 253 are controlled such that no deflection is performed, the charged particle beams 201 and 203 pass through an opening 109a of a blanking aperture 109 and reach the substrate 115.
On the other hand, by controlling the deflector 252 to perform deflection, the path of the charged particle beam 202 can be changed such that the charged particle beam 202 strikes an area outside the opening 109a of the blanking aperture 109 without reaching the substrate 115. In the present example, of the deflectors 251, 252, and 253, only the deflector 252 performs deflection. Note that all deflectors may perform deflection or any deflector may not perform deflection. A desired pattern is formed on the substrate 115 by switching whether or not each deflector performs deflection depending on the position on the substrate.
In the conventional multibeam-type charged particle beam writing apparatus, if a defect occurs in an element such as a deflector, following problems can occur.
(1) It can become impossible for a particular charged particle beam to reach the substrate 115 (irradiation is not correctly performed).
(2) A particular charged particle beam can continue to strike the substrate 115 (necessary blocking is not performed).
(3) A particular charged particle beam can be moved to an unpredictable position (position control is not correctly performed).
To solve the above problems, Japanese Patent Laid-Open No. 2005-116743 discloses a technique in which a plurality of charged particle beams are deflected all together by a common blanker located above a deflector array (on the side of the charged particle beam source), and charged particle beams are deflected by normal deflectors of the deflector array such that the charged particle beams pass through openings of a blanking aperture. In this technique, a charged particle beam passing through a defective deflector in the deflector array is blocked by a non-opening part of the blanking aperture, and thus only normal deflectors are used in forming a pattern on a substrate.
However, in this technique, because charged particle beams corresponding to defective deflectors are not used in forming a pattern, an additional wiring process is needed to obtain a complete pattern. That is, writing is performed twice to obtain the complete pattern, which causes a reduction in throughput.